Ford 347 Engine Build - Garage-Built Stroker

Here is why this is good: We ordered this Eagle, Ford 347 rotator kit online from Summit Racing and had it delivered to our front door for less than $1,000. For the money, you get a crank with an additional 0.400-inch stroke, hypereutectic pistons, and forged-steel I-beam rods. All the math and machine work is done, and the assembly is already balanced with a damper and a flexplate. The rods and bearings have been chamfered for the crank fillet, the rings are pregapped, and everything is matched so there is no interference between parts.

The most amazing aspect of the Ford 347 rotator is it can be installed while in your garage, provided your engine doesn't have massive taper in the cylinder bores, the main bearing bores are aligned and round, and the deck is flat. It means a good-running, low-mile 302 or recent rebuild is the best candidate for this swap. You should be able to add 45 inches of displacement in one weekend. You just have to be OK with the use of a die grinder, bore gauges, and micrometers.

The engine we are using for this job is the 302 we originally pulled out of a '73 Ranchero and was refreshed in the Nov. '07 issue ("Build the Cheapest Engine Possible") by JMS Racing Engines in El Monte, California. With stock heads, it made 279 hp and 341 lb-ft. Then we added a set of AFR 165cc Outlaw Street heads and picked up 92 hp and 37 lb-ft. For the final story, we added a set of pop-up JE pistons, revved the engine to 7,500 rpm, and made 479 hp and 387 lb-ft while simultaneously reaching what is likely the maximum output of an N/A 302.

We asked around about the difference between a Ford 347 and the 331 stroker kit for the 302. We heard the 331 needs to rev beyond 6,500 rpm to make the same power as the 347, making the larger engine slightly more reliable and streetable. The 347 will also make more usable torque. Machinists we talked to also claim the angularity of the rod is greater with the Ford 347, which is true. It may cause increased wear on the cylinder wall on a high-mileage engine-that is also true. On the 347, you are pulling the piston down to the bottom of the bore, increasing the likelihood that the piston will rock, as the skirts are uncovered at the bottom of the stroke. The most practical complaints are that the longer stroke requires block clearancing, the counterweight can hit the oil pump, and the rod is long enough that the piston pin intersects with the oil ring bore, possibly causing oil control issues.

Eagle fixed these problems with heavy-duty oil support rails and a tapered piston to reduce noise. Our advice is to measure everything before you order and build the thing.

29/29JMS also recommended we add a windage tray or an aftermarket pan. The extra stroke tends to dip the counterweights into the oil, causing foaming and loss of horsepower. Because the deck height is 8.200 on our block, the pistons are at zero deck. With the 58cc chamber on the AFR heads, the engine has a 10.9:1 compression ratio. That will work with pump gas and we will add a little fog of nitrous for some street fun.